1. Field of the Invention
The present invention relates to a voltage-controlled oscillator and an electronic device incorporating a voltage-controlled oscillator, or more particularly, the present invention relates to a voltage-controlled oscillator adaptable to communication devices and an electronic device incorporating the voltage-controlled oscillator.
2. Description of the Related Art
In recent years, a voltage-controlled oscillator having a frequency of oscillation that can be varied diversely has been demanded for use with various electronic devices including a portable telephone. For providing the voltage-controlled oscillator having a frequency of oscillation that can be varied diversely, a new printed-circuit board may be designed for each frequency of oscillation. However, this approach has enormous costs. According to an alternative approach, an inductive component to be included in a resonant circuit is realized with a strip line, the stripline is scraped in order to vary the inductance of the inductive component, and thus, the frequency of oscillation of a voltage-controlled oscillator is varied.
Moreover, for designing a voltage-controlled oscillator, simulation is often carried out using a computer. However, there is an error between a theoretical value determined via simulation and a measured value obtained using a prototype. A generally adopted procedure for correcting the error is to scrape a strip line included in the resonant circuit so as to change the inductance of the inductive component.
Moreover, the work for adjusting electrical characteristics such as a carrier-to-noise ratio includes scraping of the strip line included in the resonant circuit.
FIG. 6 shows a conventional voltage-controlled oscillator. Referring to FIG. 6, a voltage-controlled oscillator 3 consists mainly of a resonant circuit 31 and an amplification circuit 12. The resonant circuit 31 has one terminal of an inductor L1, which is a strip line, connected to the amplification circuit 12 via a capacitor C2. The other terminal of the inductor L1 is connected to the cathode of a variable-capacitance diode VD1. The cathode of the variable-capacitance diode VD1 is connected to a control voltage terminal a2 via an inductor L3 that is a choke coil. The anode of the variable-capacitance diode VD1 is grounded. The capacitor C2 is a coupling capacitor.
The resonant circuit 31 is connected to the base of a transistor Tr1 which functions as an amplification element in the amplification circuit 12. The emitter of the transistor Tr1 is connected to an output terminal a3 via a capacitor C7. The collector of the transistor Tr1 is grounded via a capacitor C4. A power terminal a4 is grounded via a capacitor C5, and connected to the collector of the transistor Tr1 via an inductor L4 that is a choke coil. The base and emitter of the transistor Tr1 are biased by resistors R1, R2, and R3. A capacitor C3 is connected between the base and emitter of the transistor Tr1.
In the thus-configured voltage-controlled oscillator 3, the inductance of the inductor L1 is adjusted in order to vary the frequency of oscillation of the voltage-controlled oscillator or improve the electrical characteristics thereof such as a carrier-to-noise ratio. The inductor L1 is a circuit element enabling variation of the frequency of oscillation and greatly contributing to the electric characteristic such as the carrier-to-noise ratio.
Moreover, in the thus-configured voltage-controlled oscillator 3, the variable-capacitance diode VD1 and inductor L1 are connected in series with each other to thus realize a series resonant circuit suitable for expanding a frequency band within which the frequency of oscillation can be varied. The series resonant circuit has a property that when the frequency band within which the frequency of oscillation is variable is larger than 10% of the frequency of oscillation, a loss caused by the resonant circuit 31 hardly depends on the frequency of oscillation.
In the voltage-controlled oscillator 3, the inductor L1 included in the resonant circuit 31 having the series resonant circuit and realized with a strip line is scraped using a laser in order to vary the frequency of oscillation of the voltage-controlled oscillator and to improve the electrical characteristics thereof such as a carrier-to-noise ratio.
However, since a major signal passes through the inductor L1, when the inductor L1 must be adjusted, quite delicate and very accurate adjustment is required. This poses a problem in that manufacturing efficiency is degraded. Moreover, since the major signal passes through the inductor L1, when the inductor L1 is adjusted, the electrical characteristics of the voltage-controlled oscillator 3 is likely to be degraded or the frequency of oscillation thereof is likely to be unstable. Moreover, the step of scraping the inductor L1 is needed for every product. This degrades the manufacturing efficiency. These problems become more serious when the frequency band within which the frequency of oscillation is variable is wider.
In order to overcome the problems described above, preferred embodiments of the present invention provide a voltage-controlled oscillator having a frequency of oscillation that is readily varied and an electrical characteristic thereof such as a carrier-to-noise ratio readily improved even when a frequency band within which the frequency of oscillation is variable is wide.
Other preferred embodiments of the present invention provide a voltage-controlled oscillator having a frequency of oscillation can be varied greatly without the necessity of scraping a strip line.
Further preferred embodiments of the present invention provide a voltage-controlled oscillator having an electric characteristic thereof that is not degraded and a frequency of oscillation thereof that is stable even when a strip line is scraped in order to adjust part of a resonant circuit for the purpose of varying the frequency of oscillation or improving the electrical characteristics thereof such as a carrier-to-noise ratio.
According to one preferred embodiment of the present invention, a voltage-controlled oscillator includes a resonant circuit and an amplification circuit. The resonant circuit includes an inductor having one terminal that is connected to the amplification circuit and another terminal that is grounded via a variable-capacitance diode, and a land to which a capacitor can be mounted. The first land has one terminal thereof connected to one terminal of the inductor and the other terminal thereof connected to the other terminal of the inductor.
Moreover, according to other preferred embodiments of the present invention, a voltage-controlled oscillator includes a resonant circuit and an amplification circuit. The resonant circuit includes an inductor having one terminal that is connected to the amplification circuit and another terminal that is grounded via a variable-capacitance diode, and a land to which a capacitor can be mounted. The land has one terminal thereof connected to one terminal of the inductor and the other terminal thereof grounded.
Moreover, according to other preferred embodiments of the present invention, a voltage-controlled oscillator includes a resonant circuit and an amplification circuit. The resonant circuit includes an inductor having one terminal that is connected to the amplification circuit and another terminal that is grounded via a variable-capacitance diode, and first and second lands to which a capacitor can be mounted. The first land has one terminal thereof connected to one terminal of the inductor and the other terminal thereof connected to the other terminal of the inductor. The second land has one terminal thereof connected to one terminal of the inductor and the other terminal thereof grounded.
Moreover, according to other preferred embodiments of the present invention, a voltage-controlled oscillator has a transmission line element interposed between the land and a ground terminal.
Moreover, according to other preferred embodiments of the present invention, a voltage-controlled oscillator has a transmission line element interposed between the variable-capacitance diode and a ground.
Moreover, according to other preferred embodiments of the present invention, in a voltage-controlled oscillator, the transmission line element has an adjustment terminal to change an impedance of the transmission line element by disconnecting from the ground terminal.
Moreover, according to other preferred embodiments of the present invention, an electronic device includes the voltage-controlled oscillators according to other preferred embodiments of the present invention.
As a result of the unique features of preferred embodiments of the present invention, a voltage-controlled oscillator in accordance with preferred embodiments of the present invention has its frequency of oscillation varied without the necessity of scraping an inductor through which a major signal passes. Therefore, the electrical characteristics of the voltage-controlled oscillator will hardly be deteriorated and the frequency of oscillation thereof will hardly be unstable.
Moreover, in a voltage-controlled oscillator in accordance with preferred embodiments of the present invention it is not necessary to scrape an inductor through which a major signal passes for the purpose of varying the frequency of oscillation thereof or improving a carrier-to-noise ratio thereof. Therefore, a chip coil exhibiting a high Q factor may be adopted as the inductor. In this case, the electrical characteristics of the voltage-controlled oscillator such as the carrier-to-noise ratio can be improved.
Moreover, the frequency of oscillation of a voltage-controlled oscillator in accordance with preferred embodiments of the present invention can be varied greatly by changing the capacitances of discrete capacitors mounted to the first and second lands. It is not necessary to scrape a strip line. Otherwise it is possible to reduce an amount by which the strip line is scraped. Consequently, manufacturing efficiency improves.
Moreover, a magnitude by which the frequency of oscillation of a voltage-controlled oscillator in accordance with preferred embodiments of the present invention or the electrical characteristics thereof such as a carrier-to-noise ratio can be adjusted varies depending on what portion of a transmission line element is cut. By selecting a proper portion of the transmission line, the frequency of oscillation or the electrical characteristics such as a carrier-to-noise ratio can be adjusted properly.
Moreover, a resonant circuit of a voltage-controlled oscillator in accordance with other preferred embodiments of the present invention includes first and second lands and a transmission line element defining circuit elements used to adjust the frequency of oscillation of the voltage-controlled oscillator or the electrical characteristics thereof such as a carrier-to-noise ratio. The first and second lands enable adjustment by a large magnitude. The line element enables adjustment by a small magnitude. These increase the freedom of design. Consequently, the frequency of oscillation or the electrical characteristics such as a carrier-to-noise ratio can be adjusted readily.
Moreover, a communication device in accordance with a preferred embodiment of the present invention incorporates a voltage-controlled oscillator in accordance with other preferred embodiments of the present invention that prevents degradation of electrical characteristics and has a very reliable frequency of oscillation. The communication device is therefore regarded as an electronic device achieving excellent output characteristics.
Other features, elements, characteristics and advantages of the present invention will become apparent from the detailed description of preferred embodiments thereof with reference to the attached drawings.